Current wireless communication networks typically utilize a distributed radio access architecture. For example, the Third Generation Partnership Project (3GPP) universal terrestrial radio access network (UTRAN), utilizes a distributed RNC architectural configuration as shown in FIG. 1. A serving RNC (S-RNC) 104 manages one or more user equipment (UEs) 114, 116. User and control data from an S-RNC 104 is passed directly through a Node B 108 via Uu interfaces to the UEs 114, 116 that it manages. The S-RNC is also coupled with the Core Network (CN) 100 via an Iu interface, which provides a control and user data interface to the regular terrestrial circuit or packet networks. A controlling RNC (C-RNC) 106 manages one or more Node Bs 108, 110, 112 via Iub interfaces. The Node Bs 108, 110, 112, in turn, each control one or more base stations (not shown).
In practice, any RNC takes on the role of both an S-RNC 104 and a C-RNC 106. For example, the RNC may provide S-RNC services to UEs that initiate calls with base stations coupled to Node Bs controlled by the RNC but might have roamed to other base stations controlled by other RNCs; and may also provide C-RNC services to the base stations it controls. As a general consideration, S-RNCs control UEs, whereas C-RNCs control Node Bs. S-RNCs control and receive UE measurements. C-RNCs control and receive Node B measurements.
A distributed RNC architecture is utilized so that user plane (U-Plane) data and control plane (C-Plane) data is combined within the RNC 102, for forwarding through the Node Bs, such as Node B 108, to the UEs, such as UEs 114, 116. The U-Plane is responsible for conveying user data to and from UEs. The C-Plane is responsible for setting up and removing UE connections and for implementing network signaling functions. This permits most of the complex processing to be performed within the RNC 102, thus simplifying the construction and lowering the costs of the Node Bs 108-112.
With reference to FIG. 2, a UE (such as UE X 115) may move between Node Bs 108-112 in a series of inter-Node B cell changes. Although some of the inter-Node B cell changes do not involve a C-RNC change, eventually, such an inter-Node B cell change may involve a change to a new Node B under control of another C-RNC; such as the change between Node B 112 (which is controlled by C-RNC 106) and Node B 113 (which is controlled by C-RNC 107).
It is not practical in many circumstances to move the connection between a first RNC such as RNC 1 (102) and the CN 100, to between a second RNC such as RNC 2 (103) and the CN 100 to follow a UE as it moves between Node Bs 108-113. Provisions are made to keep the connection between RNC 1 (102) and the CN 100 while permitting control of the UE by RNC 2 (103). In this case, RNC 2 (103) is referred to as a “drift RNC” (D-RNC). Communications between RNCs are conducted over a connection referred to as an Iur interface.
There is a partial control change between RNCs in that UE X 115 communicates with RNC 2 (103), which transparently passes user and control data from RNC 1 (102) to UE X 115. User and control data for UE X 115 is still controlled by RNC 1 (102) and all user and control data that goes to UE X 115, comes from RNC 1 (102). Although RNC 2 (103) does not control UE X 115 and does not know what user or control data has been sent to or from UE X 115, RNC 2 (107) controls cell measurements (via an Iub interface) pertaining to the Node B 113 in communication with UE X 115. As a result, more than one RNC controls UE X 115.
Since the CN 100 is limited in terms of how fast it can reroute the U-Plane and the C-Plane from one RNC to another, it is not always possible to synchronize the relocation of the U-Plane and the C-Plane functions from the CN 100 to the new C-RNC 107. As a result, measurements necessary to implement radio resource management (RRM) functions for UE X 115 are distributed between RNCs (i.e., RNC 1 102 and RNC 2 103). For example, the user admission control function that allows UE X 115 to establish a connection exists in RNC 1 (102), but the call admission control function that allocates dedicated resources exists in RNC 2 (103).
Distributed RNC systems are designed to handle expected or anticipated U-Plane traffic over a wireless system in a given geographic area. In large metropolitan areas, the amount of U-Plane traffic over a wireless system is often orders of magnitude greater than the amount of C-Plane traffic. Thus, U-Plane connectivity requirements generally dictate the location and number of RNCs 102, 103 that are needed to support the wireless system. RNCs are expensive hardware elements since they must support both U-Plane and C-Plane functions. The cost of providing a distributed RNC architecture escalates in regions where RNCs are called upon to handle relatively large amounts of U-Plane traffic. Additionally, in rural areas where U-Plane data communication requirements are distributed over large areas, it may not be economically feasible to provision terrestrial resources in the form of a centralized point of presence.
Another drawback with an architecture having RNCs which are distributed is that the efficiency of RRM functions is reduced. RRM functions are performed most efficiently within a single RNC that has all of the data for an RRM function available to it. For example, as aforementioned, S-RNCs control and receive UE measurements, whereas C-RNCs control and receive Node B measurements. RRM functions often require both UE and Node B measurements. In order to operate most efficiently, the RNC performing the particular RRM function should have all of the information, both uplink (UL) and downlink (DL) for all cells in UE. With the distributed architecture, one RNC will have the information for the cell-based measurements (the UL measurements) whereas another RNC will have the UE-based measurements (the DL measurements). Accordingly, a single RNC does not have all of the information required to efficiently make decisions.
Although is possible to forward or request measurements between S-RNCs and D/C-RNCs, the amount of measurement information that can be forwarded or requested is limited, and the transfer of information incurs delays. Moreover, although it is useful for RRM functions to consider measurements and channel allocations from neighboring cells, this is not always possible, in particular when a neighboring cell is controlled by another RNC.
When RNCs are distributed and each RNC manages fewer cells, less neighbor cell information is available for the performance of RRM functions. Furthermore, as the distribution of RNCs is increased across a given service area, the efficiency of RRM functions is reduced.
What is needed is an improved architectural scheme that overcomes the disadvantages of a distributed RNC configuration.